The invention relates to a process for the preparation of bead polymers.
Bead polymers are employed, for example, as ion exchangers, adsorber resins, chromatography supports, catalysis supports, polymeric reagents, imprinting polymers or as support materials for combinatorial chemistry, peptide or oligonucleotide synthesis and for cosmetic applications. The preparation of bead polymers of this type, i.e. spherical organic or inorganic particles, such as, for example, spherical silica gels, is relatively complex. Bead polymers are typically prepared in stirred-tank reactors with addition of emulsifiers, with the monomers being dispersed by turbulent pressure variations or viscous shear forces to give small droplets, which adopt a spherical shape under the influence of interfacial tension. If the reaction batch is enlarged, it becomes increasingly difficult to control the temperature programme and particle generation during mechanical dispersion. The particles formed become non-uniform with respect to their particle size distribution, and their network structure becomes inhomogeneous. Small particles below 30 xcexcm are virtually impossible to produce owing to the high dispersion energies. Alternative methods in which small particles are generated by growing nanoparticles are usually time-consuming and expensive.
A far more advantageous method, particularly for production on an Industrial scale, is performance of the reaction continuously. In this way, even large amounts can be produced with uniform product quality. In the area of bead polymerisation, there are numerous approaches for continuous reactors. The majority of the approaches use a continuously operated stirred-tank reactor, as described, for example, in various designs in Encyclopaedia of Polymer Science and Engineering, 1986, Volume 6, pages 11-18. DE 196 34 450 describes various further approaches. One possibility is offered by the use of tubular stirred reactors, which, through the formation of Taylor rings, ensure improved mixing perpendicular to the flow direction. Highly exothermic reactions can be carried out using empty tubular reactors.
However, there is still no process of this type which is used on a large industrial scale. The reasons for this are apparently difficulties in establishing the desired bead size distribution, the formation of coagulate and caking in dead spaces, and the necessity to achieve the fastest and most effective mixing possible.
It has been attempted to overcome the disadvantages described through a multiplicity of measures, such as optimisation of the reactor dimensions and use of reactors having curved to helically coiled tubes or tubular reactors having a plurality of successive bends with alternating bend direction, as described, for example, in DE 196 34 450. However, there has hitherto been no success in developing a generally applicable continuous process for bead polymerisation. The attempts that have been carried out show merely an improvement in the Bodenstein number, which is a measure of the width and symmetry of the residence-time distribution. The problems of coagulation, particle size distribution and increased space-time yield have not been solved. This applies in particular to the preparation of inorganic bead polymers.
The object of the present invention is therefore to provide a process which enables bead polymers to be prepared in a continuous procedure, with particle size range which can be set to a specific value, improved yield and more uniform quality.
It has been found that the use of novel high-performance micromixers in combination with a simple collection vessel in which the solidification and/or polymerisation reaction is carried out enables and at the same time greatly improves continuous bead polymerisation.
The process according to the invention is based on the mixing of liquid streams of suitable, usually immiscible component solutions in a micromixer, giving spherical particles in a continuous procedure with extremely improved volume yield, large particle yield with particle size range which can be set to a specific value, simplified temperature programme and reduced consumption of chemicals.
The invention therefore relates to a process for the preparation of bead polymers in which two liquid streams of immiscible or sparingly miscible component solutions, with optional supply of further component streams, are mixed in a micromixer and reacted directly or subsequently.
In addition, a preferred embodiment of the process according to the invention comprises connection of one or more ancillary devices to a first micromixer.
In addition, a preferred embodiment of the invention comprises the use of component solutions without addition of emulsifiers and protective colloids.
The invention furthermore relates to powders consisting of porous or non-porous spherical particles which are prepared by the process according to the invention and have a narrow particle size range which can be set at between 0.1 and 300 xcexcm.